"SearchAsync" InvalidCastException Null object cannot be converted to a value type - azure-cognitive-search

Question

I use Azure search and a field in the search index can be null.
Which means my code
var result = await searchIndexClient.Documents.SearchAsync<SearchEntity>(query, parameters);
throws an exception
"InvalidCastException Null object cannot be converted to a value type."
for Csharp:
public class SearchEntity{
...
boolean NewField{ get; set; }
...
}
and index document:
{
"#odata.context": "...",
"value": [
{
"#search.score": 1,
...
"NewField": null,
...
I would like to tell SearchAsync(?) to set a default value to the property in SearchEntity if the received field is null.
Is it possible?
(I know I can receive a null and default it later but what is the fun in that?)

Answer 1

One possible solution would be to define the default values in your entity and tell the JSON serializer to ignore the null values from source at the time of serialization.
For example, consider the following entity definition:
public class SearchEntity
{
[JsonProperty(PropertyName = "newField")]
public bool NewField { get; set; } = true;
[JsonProperty(PropertyName = "dateTime")]
public DateTime DateTime { get; set; } = DateTime.Now.Date;
}
and here's the code for serialization. I am using NewtonSoft.Json for that and instructing it to ignore the null values:
string json = "{\"newField\": false, \"dateTime\": null}";
JsonSerializerSettings settings = new JsonSerializerSettings()
{
NullValueHandling = NullValueHandling.Ignore
};
var searchEntity = JsonConvert.DeserializeObject<SearchEntity>(json, settings);
Console.WriteLine($"SearchEntity.NewField: {searchEntity.NewField}");//Prints "true"
Console.WriteLine($"SearchEntity.DateTime: {searchEntity.DateTime.ToString("u")}");//Prints current date e.g. "2021-07-01 00:00:00Z"